Water-insoluble fiber (which includes wheat, bran, and whole grain products) affects mainly the lower gastrointestinal (GI) tract, where it increases fecal bulk, helps to prevent constipation, and may reduce the risk of colon cancer. Water­soluble fiber (which includes guar and pectin) affects the upper GI tract by delaying gastric emptying and increasing the intestinal transport time. It may also lower levels of total cholesterol and LDL cholesterol.Although fiber’s beneficial effect on glucose level control remains unproved, eating 20 to 35 grams of water-insoluble or water-soluble fiber a day does promote evacuation and lower lipid levels. Instruct your patients who are increasing their fiber intake to do so gradually and to drink at least 8 cups of fluid a day to minimize GI discomfort.